Fact improvements & helpers

• Add FactType enum model with known (.username, .email, .phone) and unknown (.other(Int)) types of facts.
• Update Fact model properties:
  • type: Int → type: FactType
  • fact: String → value: String
• Add convenience extensions to [Fact] array:
  • func get(_ type: FactType) -> Fact?
  • func set(_ type: FactType, _ value: String?)
• Add convenience extensions to Contact model:
  • func getFact(_ type: FactType) throws -> Fact?
  • mutating func setFact(_ type: FactType, _ value: String?) throws